Since a downlink system performance of a sector boundary is seriously degraded by adjacent sector interference in a multi-sector wireless communication system, it is strictly necessary to cancel the adjacent sector interference. A base station can attain a performance gain by cancelling the adjacent sector interference through multi-sector cooperative coherent beamforming or multi-sector cooperative eigen beamforming, based on instantaneous or statistic channel information of a sector boundary user. However, since a single beamforming scheme such as multi-sector cooperative coherent beamforming or multi-sector cooperative eigen beamforming services only single user within multiple sectors in cooperation with two sectors, the number of users supportable per sector is halved and thus the overall system performance is degraded.
Hence, a multi-user multi-sector cooperative beamforming scheme such as Zero-Forcing (ZF) or Minimum Mean Square Error (MMSE) for simultaneously supporting multiple users in the sector is recently under consideration. The ZF scheme or the MMSE scheme reduces the sector interference and obtains a spatial multiplexing gain through the multi-sector cooperative transmission, and thus can address the shortcoming of the conventional multi-sector cooperative coherent beamforming or eigen beamforming. However, since the ZF or MMSE based sector cooperative beamforming scheme is solely based on the instantaneous channel information, it is quite vulnerable to a channel mismatch problem caused by a user's speed and a sounding error. Accordingly, when this scheme is uniformly applied to the sector boundary users having different channel conditions such as user's speed, not only the high-speed users cannot attain a beamforming gain but also the multi-user spatial multiplexing gain is reduced by multi-beam residual interference which increases in proportion to a transmission delay or a channel estimation error. Thus, when scheduling for the multi-user multi-sector cooperative transmission is performed without considering the performance degradation caused by the channel mismatch problem, it is impossible to select an optimal number of users and an optimal user combination for maximizing the system capacity. As a result, the multi-sector cooperative transmission performance is considerably degraded.
Hence, multi-sector cooperative transmission method and apparatus are required to reduce the system performance degradation caused by the channel mismatch problem of the user's speed and the sound error in the multi-antenna system. Also, scheduling method and apparatus for the multi-user multi-sector cooperative transmission are demanded to maximize the system capacity in the multi-antenna system.